<template>
  <div>
    <div class="menu">
      <div class="menu-left">
        <ul>
          <li
            class="menu-item"
            v-for="(menu, index) in menus"
            :key="index"
            :class="{ current: index === currentIndex }"
            @click="clickList(index)"
            ref="menuList"
          >
            <p class="text">{{ menu.name }}</p>
          </li>
        </ul>
      </div>
      <div class="menu-right" ref="itemList">
        <ul>
          <li class="cate" v-for="(menu, index1) in menus" :key="index1">
            <h4 class="cate-title">{{ menu.name }}</h4>
            <ul class="cate-item">
              <li v-for="(item, index2) in menu.sub" :key="index2">
                <a href="#" class="cate-item-wrapper">
                  <router-link class="cate-item-wrapper" :to="{name:'goods_list',params:{category_id:item.id}}">
                  <div class="cate-item-img">
                    <img :src="item.image" alt="" />
                  </div>
                  <span>{{ item.name }}</span>
                  </router-link>
                </a>
              </li>
            </ul>
          </li>
          <li class="cate-bottom"></li>
        </ul>
      </div>
    </div>
  </div>
</template>

<script>
import BScroll from "better-scroll";
export default {
  data() {
    return {
      menus: [],
      rightLiTops: [],
      scrollY: 0,
    };
  },
  computed: {
    currentIndex() {
      const { scrollY, rightLiTops } = this;
      return rightLiTops.findIndex((top, index) => {
        if (index === rightLiTops.length - 2) {
          return true;
        }

        if (scrollY >= top && scrollY < rightLiTops[index + 1]) {
          this._initLeftScroll(index);
          return true;
        }
      });
    },
  },
  created() {
    this.$indicator.open({
      text: "加载中",
    });
    this.$http.get("category").then((res) => {
      this.$indicator.close();
      this.menus = res.data.data;
    });
  },
  watch: {
    menus() {
      // $nextTick用来在下次DOM更新循环结束之后执行延迟回调
      this.$nextTick(() => {
        this._initBScroll();
        this._initRightHeight();
      });
    },
  },

  methods: {
    _initLeftScroll(index) {
      let menu = this.$refs.menuList;
      let el = menu[index];
      this.leftBscroll.scrollToElement(el, 300, 0, -100);
    },
    clickList(index) {
      this.scrollY = this.rightLiTops[index];
      this.rightBscroll.scrollTo(0, -this.rightLiTops[index]);
    },
    _initBScroll() {
      this.leftBscroll = new BScroll(".menu-left", {
        click: true,
        mouseWheel: true,
      });
      this.rightBscroll = new BScroll(".menu-right", {
        click: true,
        mouseWheel: true,
        probeType: 3,
      });
      this.rightBscroll.on("scroll", (pos) => {
        window.console.log(pos.y);
        this.scrollY = Math.abs(pos.y);
      });
    },
    _initRightHeight() {
      let itemArry = [];
      let top = 0;
      itemArry.push(top);
      let allList = this.$refs.itemList.getElementsByClassName("cate");
      Array.prototype.slice.call(allList).forEach((li) => {
        top += li.clientHeight;
        itemArry.push(top);
      });
      let bottom = this.$refs.itemList.getElementsByClassName("cate-bottom")[0];
      bottom.style.height = this.$refs.itemList.clientHeight / 1.2 + "px";

      this.rightLiTops = itemArry;
    },
  },
};
</script>
<style lang="scss" scoped>
ul {
  margin: 0;
  padding: 0;
}
li {
  list-style: none;
}
.menu {
  display: flex;
  position: absolute;
  text-align: center;
  top: 40px;
  bottom: 50px;
  width: 100%;
  overflow: hidden;
  .menu-left {
    flex: 0 0 80px;
    width: 80px;
    background: #f3f5f7;
    .menu-item {
      height: 54px;
      width: 100%;
      .text {
        width: 100%;
        line-height: 54px;
        margin-bottom: 0;
      }
    }
    .current {
      width: 100%;
      background: #fff;
      .text {
        color: red;
      }
    }
  }
  .menu-right {
    flex: 1;
    background: #fff;
    .cate {
      height: 100%;
      .cate-title {
        margin: 0;
        text-align: left;
        font-size: 14px;
        color: #333;
        font-weight: bold;
        padding: 10px;
      }
      .cate-item {
        padding: 7px 10px 10px;
        display: flex;
        overflow: hidden;
        flex-flow: row wrap;
        li {
          width: 33.3%;
          .cate-item-wrapper {
            .cate-item-img {
              width: 100%;
              img {
                width: 70px;
                height: 70px;
              }
            }
            span {
              display: inline-block;
              font-size: 14px;
              color: #333;
            }
          }
        }
      }
    }
  }
}
</style>